Higher intake of β-glucan impairs reproduction in a female teleost, Tor putitora (Hamilton, 1822)

Although the immuno-modulatory and stress-relieving properties of beta-glucan is well elucidated in humans and other animal models, including fish, its role as a dietary supplement on reproduction is extremely scarce. Therefore, in this study, adult female fish were fed one of four test diets having 0 (control), 0.5, 1, and 1.5% beta-d-glucan for 130 days and its effect on reproductive performance, ovarian and liver histology, sex hormones, and transcript abundance of selected reproduction-related genes was assessed. Low dietary intake of beta-glucan improved fertilization and hatching rates (p<0.05). The relative fecundity and percentage of spawning females were higher (non-significant) in 0.5% beta-glucan-fed groups. Surprisingly, even after 130 days, spawning did not occur in 1.5% beta-glucan-fed individuals. Irrespective of beta-glucan intake, all the brooders recorded similar plasma 17 beta-estradiol and maturation-inducing hormone (p>0.05). Higher intake of beta-glucan (1.5%) upregulated aromatase genes without a parallel increase in 17 beta-estradiol. However, plasma vitellogenin increased with increasing beta-glucan up to 1.0% then declined at 1.5% (p<0.05). The fish that received control, 0.5, and 1.5% beta-glucan recorded similar vitellogenin levels in their plasma. Significantly higher plasma cortisol was evidenced in 1.5% beta-glucan fed brooders (p<0.05). Histologically, higher follicular atresia and leaking of yolk material was evidenced in 1.5% beta-glucan-fed group. Liver histology revealed the highest nutrient/lipid accumulation in fish that received 1.0% and 1.5% beta-glucan. This study demonstrated the stimulatory effect of beta-glucan intake at a lower dose (0.5%) on reproduction. However, higher intake (1.5%) could perturb normal reproductive function in a fish model and caused an increased number of atretic follicles leading to spawning/reproductive failure.